Rollup merge of #73339 - jonas-schievink:unbug, r=estebank

Don't run generator transform when there's a TyErr

Not sure if this might cause any problems later on, but we shouldn't be hitting codegen or const eval for the produced MIR anyways, so it should be fine.

cc https://github.com/rust-lang/rust/issues/72685#issuecomment-643749020

src/librustc_mir/transform/generator.rs

@@ -1222,7 +1222,11 @@ impl<'tcx> MirPass<'tcx> for StateTransform {
                     movability == hir::Movability::Movable,
                 )
             }
-            _ => bug!(),
+            _ => {
+                tcx.sess
+                    .delay_span_bug(body.span, &format!("unexpected generator type {}", gen_ty));
+                return;
+            }
         };
 
         // Compute GeneratorState<yield_ty, return_ty>